TSP #15 - Tutorial on the Theory, Design and Characterization of a Single Transistor BJT Amplifier

[@mlee3273]

At 7:09, you consider Signal Swing. I think the same clip is repeated at 9:33 to 11:56, which you could delete. Very good lesson. Enjoying trying to keep up! Cheers. Matt

[@m1geo]

Agreed. The clip repeats twice!

[@iamgrimjmnt9590]

I'm an Electronics Engineering student and I found this VERY helpful.

[@Thesignalpath]

My expertise is in mm-wave integrated circuits for wireless and wireline applications. You can lookup my work and publications through Google Scholar. I have also been playing with electronics for 20 years, since I was 10 years old.

[@billmoran3812]

The Signal Path I like that you began playing with electronics at 10 years old. I did the same. I've been an engineer for 45 years. I'm 66 years old and still learning. The more I know, the more I realize that I don't know.

[@ufohunter3688]

Dear Professor Shahriar, I want to build a system where I can monitor all radio frequencies at once, within the 10-20 mile radius? Is there a way a hobbyist can do that with say dozens of SDR USB Dongles and a few Raspberry PI3s? Self-financing has that "being poor" side-effect. I have already made the most sensitive 3D Geiger counter possible with SI-22G tubes. Also a Light spectrometer using plans from the internet (public Labs). They work great. I am currently working on computerizing my 6" Newtonian telescope, and attaching one color and one IR RPI cameras, green 500mW laser pointer, Spectrometer,... to be attached to the body of the telescope. So, when I aim at an object with the laser, I would see it in both cameras, the telescope, and the spectrometer. The Chilean and US Navy videos on those UFOs, has proven to me they exist and gathering scientific data, is the only way to go towards figuring out what these things are, and how they work. Can you provide some guidance as to the easiest/cheapest way for a technologist to detect and record local EM anomalies to be studied later? Merci. Khoda Hafez.

[@pitot1988]

@@ufohunter3688 By all radio frequencies at once, what are the frequency range you are talking about?

[@SiriusFuenmayor]

Could you make a tutorial explaining the basic elements of a RF digital transceiver such as a Bluetooth or WiFi modem?

[@nidhinbenny7975]

@@billmoran3812 Its nice to hear that someone so experienced keeps learning. I only really started messing around with electronics about 2.5 years into my degree (I would have been about 24 around that time) and was sort of angry at being so lost - I thought I should be able to understand it all since I'd been studying it all in uni. Lately though, I'm starting to appreciate that this stuff can be really hard, and that there is no substitute for spending a lot of time, reading, watching, doing, making mistakes and learning. Hope to be a lot better at this stuff one day! Electronics is awesome.

[@chironjo]

This is a very nice lab exercise that I wish I had back when I was working my BSEE. I bet some of my professors hadn't designed one amplifier and were teaching amplifiers theory!

[@Thesignalpath]

Thank you, I will correct the problem. Yes, the 10nF is calculated for low-pass operation. If you want to only use transistors, you can design another common-emitter stage to follow this one. Just make sure you don't use an emitter capacitor again the whole thing would become very non-linear.

[@analogzeke3924]

That RC=RE is a compromise to achieve beta-insensitive biasing (I called it Iq accuracy, but beta-insensitivity is a more precise description) while maintaining signal swing is understandable, though I felt it wasn't made clear in the video; in the context of the VRC=VRE discussion (12:00), it would seem as if RC=RE is optimal for maximizing signal swing. The importance of the distortion is largely a matter of taste, and of course, what the amplifier will be used for. Love your vids, keep it up.

[@pedrogonzalezgil]

I also find that explanation a little lacking, more after having been watching other videos searching for a more in-depth answer on why are Rc and Re chosen as they are, and finding conflicting answers. Absolutely think this video is gold, no intention to devalue it a bit. Thanks Shahriar!!

[@MarkG80615]

This is one of the clearest explanations of theory that I have ever seen in decades of working as an Electrical Engineering Tech. Good Job! Keep up the good work.

[@GeezerDust]

As I'm not an engineering student, most of this was over my head. However, I believe I can use your excellent video to construct a simple audio amp. Thanks, you're a great teacher.

[@alextrofimov7947]

Great video! Just a little correction. Human ear can perceive sounds down to 20 Hz, but for a microphone amplifier 50 Hz may be a rather good threshold to pick up less hum and different mechanical noises, wind for example. Humans can actually perceive frequencies less than 20 Hz not as sound, but as vibration. It could matter for say a good studio mike. If somebody would record say a sound of arriving train, it would be rather dissapointing to not have this vibration low-end in the record. This details don't really matter for the purposes of this video of course, but I thought it may be interesting.

[@robertw1871]

Some people can hear below 20Hz and spectral content above 20kHz also plays a role in signal shape at far lower frequencies, we always designed for 5Hz-100kHz, but with EQ on the passband gain. RIAA is a good starting point, most people prefer a smiley face curve : ) so shelving filters are good for the general public. You’re correct, design for flat response across the range will sound terrible to most people even though it’s technically perfect...

[@freon500]

Thank you for sharing your insights and understanding as you have in this video. I've been looking for a simple one transistor amplifier circuit that actually works when I build it and here with you I have gotten so much more. I'll probably post something after I build it.

[@Thesignalpath]

I teach this material at the beginning of an Analog Electronic course in fourth year of an EE bachelor degree or first year masters degree depending on the university.

[@zetaconvex1987]

That seems like quite a late time to teach this?

[@AissaAzzaz]

@@zetaconvex1987 we study it in the second year but our bachelor degree is only 3 years

[@Thesignalpath]

My calculations of the signal swing is correct. Perhaps what you are trying to say is that the signal swing can be improved. That is true. However at the cost of causing more beta-sensitive biasing. Dividing the signal equally between the three elements is a compromise between beta-insensitive biasing and swing. Furthermore, it is true that there is no emitter degeneration. However for an application where the input is less than VT (25mVpp), the distortion is not of significant importance.

[@sameersharma4038]

Due to availability, I would have to make the 1st stage amplifier with following component values: BC 547, Rc=Re=1k, RB1=14k, RB2=10k, Cc=0.1uF, Cb=Ce=100uF Will the amplification calculation (i.e. A=-64) and the practical results (i.e. Vin=5Vpp, Zin=50, f=2.5kHz, Vout=300mVpp) hold (under experimental error allowations)?

[@scott2e]

THIS VIDEO IS GOLD! Only wish I found this last year.....

[@Thesignalpath]

The dual +/- supply is common for analog circuits. It also makes using the opamp easier as a second stage amplifier. A single +5V supply can also be used. The same principles apply.

[@freon500]

I built the circuit and it works! I'm still working on the input because my function generator's minimum output voltage is too high (reducing the amplitude of the function generator to milivolt range is a project right there). Today I'll try a microphone. If you want to build on this basic circuit adding a second transistor or what ever it would be much appreciated. Anyway, Shahriar thank you again for this very helpful video.

[@eskilstuna0123]

Very nice explanation. The information you give makes the topic less abstract and more concrete.

[@lcradan24]

Excellent video! Im not an engineer but i understand some of the theory. As always, u have a great method of teaching and explaining electronic things. I hope to see more new videos as your content is possibly one of the best out there. Thank you Sir.

[@davidgana2855]

Wish we had more tutorials like these from you.

[@dimitrisspiridonidis3284]

seriously i have read 3 college books and watched a lot of lectures and they all fail to ex-plane properly what role that capacitor is having in that circuit. good job man god bless you

[@RavenLuni]

I've been trying to get my head round this subject for ages. All of the explanations I've seen have so much essential information missing. This video is the final piece of the puzzle I needed to understand it. Thankyou :) So far, this is the only one I've seen that properly explains signal swing and what VCEsat is. I had to look up what gm and Vt were though - never heard of those before.

[@PauloConstantino167]

You are magnificent. You are unique on youtube on how good and indepth your videos are. Bless you!

[@carmelpule6954]

By putting Re the biasing becomes independent of Beta, and so does the DC gain, which in this case it is equal to unity as there is a lot of negative feedback. On putting the capacitor Ce the AC gain is still dependent on Beta. I like the manner in which you found this maximum gain. THis AC gain I presume may be controlled by adding another resistor above Re, unbiased by Ce.

[@miceuz]

Nice video, thanks! Just I didn't understand what is Vt and where it comes from.. Could you explain that?

[@joshhyyym]

That has got to be the neatest breadboard I've ever seen, and a brilliant tutorial.

[@Lobstermagnet5]

You're extremely talented at making these concepts easy to understand. Great video!

[@pepe6666]

thank you very much. it would be great to push white noise through this so we can watch the frequency response. its fascinating looking at the low passing because it wasn't a very wide Q. i'd really like to see a video analyzing the noise of this circuit. that'd be amazing. thank you for making this. you're the man

[@gio-ky9nh]

Thank you so much for the great tutorial. I don't think you'll ever know how valuable it's been. Keep up the great work!

[@gio-ky9nh]

I finally understand why Re, Ce, and Cc are needed (most just hand wave this part) Thanks for the clear explanation.

[@Thesignalpath]

You are welcome.

[@neodonkey]

learned more in this one video than all the other stuff I have read on this subject combined. Great job!

[@RachitSrivastava96]

Thanks a lot for this :) Cleared all doubts and helped me to organize all the equations and tools I had learned theoretically to practically build an amplifier.

[@cooper7655]

This video was very informational until 17:00 when you suddenly added components without their explanation. When you show with the equation how Re is selected to create a bias which is beta insensitive, as well as showing the equation which shows how Re affects the gain, these were very helpful. However, I lost interest when you began to neglect the equations for the decoupling capacitor, voltage divider, and the collector capacitor to limit bandwith. I would have liked to see the collector capacitor and bandwith equation most of all. Thanks for the first half though.

[@jeffreymelanson9230]

The Offset Volt has some well explained videos on the subject. As a starting point a BJT has two modes of behavior a DC and an AC mode. The BJT first has to be biased (setup) using resistors and DC voltages. Afterwards, it can be used to amplify AC signals using capacitors and resistors. When you come across variables using capital letters they refer to DC parameters lowercase refer to AC parameters. Essentially, the DC voltages setup the BJT to be used as an amplifier. You use all those weird equations with the uppercase letters to accomplish this. Once this done, you can add capacitors and more resistors to amplify your AC signal. This is done using the equations with the lowercase letters. You wind up with two different circuits connected onto the BJT an AC circuit and a DC circuit. This clever trick is accomplished via the capacitors.

[@pepe6666]

@@jeffreymelanson9230 thanks for that bit of info. im gonna be rewatching this like a billion times over the next few years as i gradually learn more. kinda sorta getting there.

[@asunasposibol]

@@jeffreymelanson9230 thanks for the feedback!. So 2.5*Rb2/(R1+Rb2)= 1.046 Volt to the base. Any clue on why this 1.046?

[@Thesignalpath]

Vt is the thermal voltage and is equal to KT/q. This is a physical constant.

[@Atlascol]

Good Video and thank you. In the video, you repeated the signal swing section at 7:15 and 9:32 otherwise is perfect. About the design, Did you calculate the 10nF capacitor like a low-pass filter with the collector resistor? and if I just want to use transistors (without a op-amp), Do I have to use a common collector stage before a common emitter stage?

[@zorabixun]

Hi, very interesting, i am surprised how the mathematical theory can be close to the later practice and measurements on electronic I have a question to modify this project. I would like to receive only positive, top part of the amplitudes, but the amplitudes don't come down to zero, only stop for example on +0.5V before zero, and again rising up .... It could be done with 4 diodes to take also use of the lower amplitude .... Thanks for any suggestions

[@imtzaii]

Just jumping into all of the design stuff and I really love it. Fine job on the video and the content. As Joshua mentioned as well, that breadboard layout was very clean. I'll be back for more.

[@mohammadhajibeigy3284]

Excellent job Shahirar, Great English and very good explanation in details with good speed!

[@10gaugesbelow]

how do we know what RB and RE are to calculate the first equation?

[@mohammedtalha4649]

I hope you make more of such videos. Going into design and development of electronic circuits

[@aerofart]

Transistor calcs are confusing! Great tutorial. Want more like this!

[@t1d100]

I really enjoyed your thought process and approach. Thank you for all your efforts to teach us.

[@jeromequelin]

Thank you for this, I love your design videos, especially those that go "back to basics". Cheers!

[@hyperboogie]

Great video but there's something I would like clarified: I understand that we want the maximum voltage swing and I understand why VRc should equal Vce-Vsat but I don't understand why we also want them to equal VRe. Why Can't we have VRc = Vce-Vsat and keep VRe smaller?

[@neelkamalsemwal4072]

Hey, if u still haven't found the answer, then here is what I understood : To maximize the upswing, u have to maximize VRc which itself has Vc (voltage at C) component (i.e. VRc= VR-VC) and now to maximize VCE, U have to maximize both VC and VE (see both are of opposite sign) which in turn makes u increase VRe. so, what basically it means is that maximizing one of the voltage has an effect on the other.

[@EdwinFairchild]

im confused as to why he is using a negative voltage, ive always seen these examples use regular positive voltage and ground and you set Voltage at the collector to be half of your power supply which puts it right in the middle of the load line

[@jeffreymelanson9230]

BJTs have a great deal of variability when it comes B-values (Beta) they are also affected by temperature changes etc this means that the gain will also be affected by these factors. They are biased so that they operate at a certain DC current and DC voltage. In other words a certain operating point. There are different types of biasing configurations that attempt to attenuate these variabilities and thus provide a stable operating point. This type of biasing does just that better than the biasing you are more familiar with.

[@DD4DA]

A very good explain and demo... thank's alot for your work...

[@pychneag]

Excellent video. Some of the math/theory was over my head but I followed along okay. Thanks again!

[@joblessalex]

Is it possible to make a tutorial on rf amplifiers? I can't find one anywhere!

[@SirEngelmann]

Thank you for uploading this very helpful video. I finally found a video which uses the same notations and abbreviations as the university I study at does. Greetings!

[@ivanreynoso3849]

You should make more videos like this one. I love theory/design videos. Thank you, and keep it up!

[@lalleyatata]

All I got is love for you thank you for teaching me how to build a circuit and all the potential that came with good cookie stuffed

[@gamccoy]

This was a terrific video! The only thing that could have made it better is if you used a hybrid equivalent diagram to explain the Q-point voltages. I also have to say I am green with envy at your lab; you have lots of nice toys.

[@YukunKennyRen]

This is one of the best tutorials. very clear.

[@omnicrutch]

VT = 25mv @ room temp or 1/.025=40 makes sense...but where did VT come from, i'm sure its on the data sheet for the 2n2222A, but this was the only part I feel wasn't super clear, and seeing the data sheet referenced i think would help move things along, otherwise great video, thanks!

[@SJayanth]

12:25 why do we want to maximise the voltage across Re? I understand that Re should be high for beta independent biasing thus also V(Re), but should it be as big and same as voltage across Rc? Many thanks for the video.

[@robertpendergast2620]

Have you done or plan to do a video on setting this amp's PS to be a single (5V, gnd) instead of split supply? What needs change if I want to use a 9 or 12V supply? Thanks. You are a great teacher and thanks for the notes too.

[@DallasPrincessAngel]

Thanks for the good clear explanation. I noted that you're using a BJT for the first stage to avoid noise, but then you use an opamp for the second stage. Would the noise come from the large-value feedback resistor required to get a gain of 100 out of an opamp? Is that also why you used a non-inverting opamp configuration, to use a smaller-value feedback resistor? Thanks.

[@garysmith1532]

Just picked this up, excellent, I was getting on fine until the RC,RE calc, cant see how you got to 800ohms, :-(

[@nandakishorebilla3213]

Mr.Signal Path have a small doubt where it comes from rc/beta.Could you please explain

[@Thesignalpath]

The noise was actually from the oscilloscope. There was a problem with the beta firmware I was using. The noise is not from the circuit. :)

[@WhiskeyRichard.]

You mentioned noise compensation biasing optimization, could you clarify or make a video on that at some point? That and/or differential amplifiers

[@shantk7378]

Nice video, but some important information is missing. How did you derive 14 Kohm for RB1 and 10 Kohm for RB2?

[@berkkucukoglu7332]

This is a nice way of designing an amplifier. However, there is also the S-parameter method. What is the link in between these two methods? It confuses me because here you are designing for voltage. With S-parameters we design for power. Furthermore, couldnt you just get this voltage amplification with a transformer? I am confused about multiple points, and will be really happy if you can help me

[@oddball0045]

What do the variables gm and Vt mean?

[@carriersignal]

gm refers to transconductance, it is essentially the ratio of output current change to input voltage change. Vt is the thermal voltage and is derived from certain constants at room temperature, taken to be ~26mV give or take.

[@sssttt6533]

carriersignal thanks for your explaination

[@stonail665]

Thank you for this.Please do more of this stuff (analog audio & Synthesizer) .

[@DoDyX66]

Whats is the voltage that you need at yo base? at 18:25 How do i know what i need? in your case what is the voltage that you need at your base?

[@cattflap1447]

5 years late, but .... voltage at RE is 1.6, the base voltage must be .6 higher so 2.2v. This is a dual supply so 2.2 - 2.5 = -.3v at base.

[@nagytibi95]

My question is that the first bipolar stage of the amp is phase shifting the input singnal, and the second stage is configured to be non-inverted, so the output signal is inverted according to the input signal. This can be solved if we configure the second stage for inverting the signal? Sorry if this was mentioned before. Thank you for the great educational videos!

[@lucasng3330]

the young Shahriar :)

[@bayviewboom4468]

3:08 What's common emitter voltage? Update: oh, ok, you corrected yourself, it's collector-emitter. So what do you mean "not good for an amplifier"? Why not good?

[@yaghiyahbrenner8902]

Shahriar where are you man?, what's keeping you so busy? we miss you when are you returning ???????

[@Ruddy761]

Well done tutorial. One question though. How did you choose the bias voltage? (RB1 and RB2)

[@fabiomonteiro9298]

First I'd like to thank you for all the amazing content you've been shared with us! My question is why the input and shunt capacitors are polarized type (eletrolytic)? They shouldn't be unpolarized ones because the alternating voltage? Best regards from Brazil!

[@joaoLucasProtocoloJ]

It's because of the values. High capacitance values are just available for electrolyte cap types or for tantalo types. The electrolyte ones are less expensive and easily available. Hello from Brazil!!

[@flyingfrancisco]

Hi This is probably the best explained transistor tutorial on KZbin . may I ask you why you chose to have a negative voltage. I am new to transistors and would appreciate your explanation. Thx

[@youpattube1]

At about minute 7 you set up your equation. In it you said Ie =Vb + 2.5 , etc. But you pointed at the -2.5v at the bottom. Which is right, 2.5 or - 2.5 ?

[@poochie1480]

Great work .nice equipment

[@2326TOM]

Thank you for your time and your skills. i'm aware that these videos take allot of time to make.But if you can, can you do a video on explaining a bjt transistor datasheet. Thank you.

[@frankking5326]

Great job man! The signal is beautiful.

[@anvintj]

Good work. Design is wonderfully explained!

[@billigerfusel]

What values did you chose for the 20kHz BW and the CB?

[@sin6city6stories6]

How much power can be taken from the first stage BJT amplifer if I were to hook it up directly to a small speaker (or maybe even earphones). As well as if I were to connect the earphones to the second stage.. great videos by the way very well done

[@daniellybaert1958]

Once again, perfect tutorials, thanks, thanks.

[@richardneifeld7797]

Very useful. Thank you.

[@shritwikbhaduri3135]

hello sir am not very familier with the analog circuit design so i find difficulty in relating the base circuit to the emitter collector network.my doubt is how did you get the values of base resistors i.i r1 and r2?

[@topherteardowns4679]

Beautiful. Love your show!

[@flyingfrancisco]

Hi in your final schematic are Rb1,Rc and Cc connected to +2.5 volts and Rb2 ,Re and Ce connected to -2.5 Volts ?? Thx in advance

[@muhammadyounus7143]

Design a circuit using BJT for switching of a DC load. Load comprises of 5kW at a voltage of 200V DC. Represent the load with a resistance. Available stock of BJTs have βDC of 100, 120 and 150. Switching should be performed using a 12V battery Plz tell how can i design

[@ggattsr]

Outstanding video as usual. Thanks for sharing.

[@jimadams2473]

Excellent instructional video. Thanks

[@FungSit]

Can you make a sequel video showing the a/d converter and power opamp is added so it drives speaker? That would be more complete and motivating. By the way, what opamp did you use in this video? Does it use two power source or one?

[@congi]

Very clear and informative! Thanks!

[@acatisfinetoo3018]

I wanted to get into designing my own circuits, but all these equations are so hard. I know a fair amount of algebra and calc, but I just can't grasp the process of designing a circuit from scratch.

[@laharl2k]

nice video, this was one of the things i was missing to learn

[@ninjaman1138]

what do i have to learn before i can understand this. im trying to learn electronics. i am studying a level 3 course, and intermediate radio course. i dont know any of this. what degree covers this stuff please

[@mnVishwas]

Loved it mate... :) Keep up the good work of helping us.

[@DJTrancenergy]

I'd love a tutorial on circuit techniques to lower the noise of an amplifier

[@Sctronic209]

Are RE and RC even became this is a dual supply?

[@janbrixcastillo1152]

this is very helpful. thank you so much!

[@markmarfega5019]

can you give an preamp circuit design with the parameters and procedures??

[@ahmadkadahsalim5048]

I've really enjoyed in this Video, thank U for this Explanation

[@saeedsobhani1981]

Beautiful, I am impressed, how may I follow you?

[@meraydin1]

Can you share the design and dimensions of your workbench?

[@MatrixOfDynamism]

what is your background that you know the Analog stuff or should I say electronics so well? I have done a degree and the analogue stuff was too much vague. None of the teachers that taught me were analogue electronics specialists as far as I can say. They did know enough and have a PhD to be teaching in the University though.

[@AelmRahc]

You set Ic = 2mA, how did you come up with that value? please ^^

[@tanaka77blenderexcersies74]

I know this is very old, but how did you solve for Rb1 and 2? I lost the plot there... Can anyone help?